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WOLF BLITZER, CNN ANCHOR: Happening now: a potential game changer in Syria's civil war, the Obama administration revealing it is now revisiting the idea of arming the rebels.

Plus, hard-partying pals, new information about the relationship between the Boston bombing suspect Dzhokhar Tsarnaev and the friends accused to trying to cover his tracks.

And new leads on the possible cause of a fiery 747 crash, deep concerns about the cargo and whether a disaster like this could happen again.

I'm Wolf Blitzer. We want to welcome our viewers in the United States and around the world. You're in THE SITUATION ROOM.

The rocket-fire in Syria intensifying, and government troops on the offensive right now. Activists say the regime's forces have made gains in the city of Homs and have committed what they describe as a massacre in a coastal village.

As Syria's civil war takes another deadly turn, U.S. policy may be turning as well. There could be a turning point for the Obama administration. The defense secretary, Chuck Hagel, saying the Obama administration is now reconsidering whether to arm Syrian rebels.

BARBARA STARR, CNN PENTAGON CORRESPONDENT: Wolf, we had a press conference here in the Pentagon. Everybody knew behind the scenes that the White House was rethinking this. But the White House had not come out and said it. You just saw in Mexico the president would not be specific. Today, Chuck Hagel decided it was time.

We pressed him, is the administration rethinking its opposition to arming the rebels? Listen to what he had to say.

(BEGIN VIDEO CLIP)

STARR: So you are rethinking the -- the administration is rethinking its opposition to arming the rests?

CHUCK HAGEL, U.S. DEFENSE SECRETARY: Yes.

STARR: And may I ask, why? What has changed in your mind, and does this put you, respectfully, at odds with the U.S. military, General Dempsey, who said it's not a good idea in his view? Why are you rethinking arming the rebels?

HAGEL: You look at and rethink all options. It doesn't mean you do, or you will. These are options that must be considered with partners, with the international community.

(END VIDEO CLIP)

STARR: Now, Wolf, no decision has been made. This is very clear, this is very precise. They are rethinking whether they want to lift their opposition to arming the rebels. No decision has been made.

But, look, the White House is under considerable pressure from some in Congress to do something as the carnage goes on in Syria. They're going to look at it. As the president indicated, they have to decide, could it really help? There's a lot of concern, if they provide these weapons, whose hands they really will fall into -- Wolf.

BLITZER: And I know the Israelis are pretty concerned as well that some of these high-tech weapons, if you will, these sophisticated weapons could wind up in the wrong hands. What are you hearing about that?

STARR: Absolutely, Wolf.

Just yesterday, the U.S. -- the ambassador to the United States from Israel, Michael Oren, someone you frequently have on THE SITUATION ROOM, told me that Israel has now asked the White House to vet, to make sure when they -- if and when they decide to supply these weapons to the Syrian rebels that they don't fall into the hands of terrorists, al Qaeda, Iranian militia members operating inside Syria.

That will be very tough to do. All of those elements are across Syria. Israel, one of the U.S.'s closest allies, very concerned because al Qaeda elements in Syria are already on its northern border -- Wolf.

BLITZER: Barbara at the Pentagon, good Q&A today with the secretary of defense. Thanks very much.

Let's go to Syria right now, where one Syrian official is talking exclusively to CNN about chemical weapons, the use in the civil war in Syria.

He spoke to our Fred Pleitgen, who is joining us now from Damascus.

Rare to have a Western reporter in Damascus. You're there, Fred, for us. Tell our viewers what the reaction is, first of all, to what Secretary of Defense Hagel said today about the U.S. rethinking arming the rebels.

FREDERIK PLEITGEN, CNN CORRESPONDENT: Well, it certainly is something that caused a lot of concern, especially among the Syrian government.

As you said, I spoke to the information minister of Syria today, and he went out to great lengths to say that his government, that his military had not used chemical weapons in the ongoing conflict.

In fact, he blamed Islamist rebels for using these weapons. He said that those weapons had come through Turkey. He even blamed the U.S. for allegedly facilitating that. Let's listen in to what he had to say.

(BEGIN VIDEO CLIP)

PLEITGEN: The United States says that it has evidence that chemical weapons were used in the conflict here. Did your armed forces use them?

OMRAN AL ZOUBI, SYRIAN INFORMATION MINISTER (through translator): The government would never use chemical weapons if we had them. We have proof that Islamic Jabhat al-Nusra have used chemical weapons.

America is not serious about discussing this type of chemical weapons used. They want to accuse Syria and not search for the truth. It is shameful.

PLEITGEN: Do you fear that this could draw the United States into increased action?

AL ZOUBI (through translator): The most important question is why Western countries are given such weapons to al Qaeda and Jabhat al-Nusra.

Do they want to increase terrorism, or do they want to find a pretext to invade Syria? If they're trying to make them stronger, it means that the Western countries are on the same side as the terrorists.

PLEITGEN: I will give you President Obama's position then, because President Obama is taking a lot of heat in the United States for not taking more action on Syria. How do you view his approach?

AL ZOUBI (through translator): If President Obama says chemical weapons are a red line, then he is in direct accordance with President Assad, who also thinks that chemical weapons are a red line.

(END VIDEO CLIP)

PLEITGEN: So, Wolf, I'm not sure that the administration would agree that President Assad and President Obama see eye to eye on any of these issues. However, the information minister also telling me at this point in time the Syrian government will not allow a U.N. team to enter the country and have blanket access to anywhere here to check out any of these...

BLITZER: Fred Pleitgen, we got some technical issues there. But he's in Damascus. Thanks very much for that.

We just heard moments ago the president once again saying Bashar al-Assad, the Syrian president, he must go.

And the NATO secretary-general, Anders Fogh Rasmussen is here in Washington.

Secretary-General, thanks very much for coming in.

ANDERS FOGH RASMUSSEN, NATO SECRETARY-GENERAL: You're welcome.

BLITZER: So, do you think NATO, the NATO allies should arm the rebels in Syria?

RASMUSSEN: First of all, let me stress that NATO as an alliance doesn't impose arms embargoes, nor do we deliver weapons. That's for nations to decide.

But I agree with Secretary Hagel that the international community as such must consider all options to bring an end immediately to the bloodshed in Syria.

BLITZER: Including providing lethal weapons to the rebels to fight the Bashar al-Assad regime?

RASMUSSEN: I think that there are a lot of dilemmas that have to be considered closely.

The goal must be to bring an end to this bloodshed immediately. And, of course, there are two sides of delivering weapons. One side, of course, is that you can strengthen the hand of the opposition, and that way force the regime to negotiate. The other side, of course, is the risk of proliferation of weapons, and that they fall into the wrong hands.

BLITZER: How worried are you that some of those weapons would fall into the hands of al-Nusra or al Qaeda supporters in Syria?

RASMUSSEN: Obviously, it is a risk.

But, of course, the international community must do what it takes to bring an end to this bloodshed. But my bottom line is that the best way forward is to find a political solution. To that end, we need a strong and unified message from the U.N. Security Council.

BLITZER: Would a political solution allow Bashar al-Assad to remain in power?

RASMUSSEN: Realistically speaking, I don't think so. I think the best framework for a political solution would be the declaration that the Action Group on Syria published on the 30th of June, 2012.

The strength of that declaration is that all five members of the permanent members of the U.N. Security Council signed, including Russia and China, and I think building on that, it should be possible to find a political solution.

BLITZER: Do you believe Bashar al-Assad's forces have used chemical weapons against their own people?

RASMUSSEN: As a matter of principle, I never comment on intelligence reports. But, obviously, there are indications that chemical weapons have been used. However, we don't know the detailed circumstances, and we don't know by whom they have been used.

BLITZER: So, is it possible, as the Syrian regime claims, that the opposition, the rebels were using chemical weapons?

RASMUSSEN: I think you can't exclude anything at this stage. I also think recent history demonstrates how important it is that we are very careful in the handling of intelligence when it comes to the possession of and possible use of chemical weapons.

BLITZER: You're talking about the bad intelligence leading up to the war in Iraq, where the U.S. and others claimed Saddam Hussein had weapons of mass destruction stockpiles that were never found.

RASMUSSEN: I think that should be taken into account. And that also explains why political leaders are so careful when it comes to the handling of such intelligence.

BLITZER: Explain why NATO got involved in getting rid of Gadhafi in Libya, but is not getting involved in getting rid of Bashar al- Assad in Syria.

RASMUSSEN: There's a very clear difference between Libya and Syria.

BLITZER: What is it?

RASMUSSEN: In Libya, we operated on the basis of a clear United Nations mandate to protect the civilian population against attack, and we had active support from countries in the region. None of these conditions are fulfilled in Syria.

BLITZER: So your impotent right now, NATO, because the Security Council has not passed a resolution authorizing the use of force to deal with the crisis in Syria?

RASMUSSEN: That's, of course, one very important aspect.

Any action requires a sound legal basis. On top of that, Syria is a very complex society, and this conflict has a lot of regional consequences. And any external military intervention might have unpredictable regional consequences.

BLITZER: Still ahead: Would the NATO secretary-general actually meet with North Korea's Kim Jong-un? The NATO secretary-general was just in the Korean Peninsula. You're going to stand by and hear his surprising answer to my question. That's coming up later this hour.

Also, the party life of the Boston bombing suspect -- an inside look at Dzhokhar Tsarnaev and the friends accused of covering up for him.

(COMMERCIAL BREAK)

BLITZER: Two weeks after Tamerlan Tsarnaev died in a shoot-out in police, the Boston bombing suspect's body has now been claimed.

The medical examiner says someone will pick up the body at the funeral home this evening. He won't say who that is. We're told the cause of death won't be released until his death certificate is filed. That could happen tomorrow morning.

Meanwhile, Brian Todd is joining us now from the Boston area. He's got more on what happened today -- Brian.

BRIAN TODD, CNN CORRESPONDENT: Yes, Wolf.

We're told that the body of Tamerlan Tsarnaev has been claimed. The medical examiner's office not saying who claimed the body, and not releasing the cause of death, as you mentioned. That does not come until the death certificate has been issued. A lot of speculation as to who might claim the body, whether it would be an uncle, whether it might be one of the sisters. We do not know at this point.

Meanwhile, new information tonight on just how close the four young men were, the other young men involved in this investigation, the three suspects arrested yesterday and Dzhokhar Tsarnaev. It was a bond that brought them all together at this college and ended up with all four of them jailed.

(BEGIN VIDEOTAPE)

TODD (voice-over): They could relate to one another from the start, Russian speakers, immigrants trying to assimilate into American life. But one of them had been at it longer, and the other two gravitated toward him.

(on camera): Dzhokhar Tsarnaev, friends and acquaintances say, was fully Americanized, could move easily in different circles. But Dias Kadyrbayev and Azamat Tazhayakov from Kazakstan struggled with English and with school here at UMass Dartmouth.

(voice-over): Kadyrbayev's lawyer says he befriended Dzhokhar Tsarnaev because Tsarnaev had been in the U.S. for a long time, spoke English well and knew the ropes.

But Raja Nageswaran, a fellow student at UMass Dartmouth, says despite their dependence on Dzhokhar, the two Kazakh students could still create a stir on their own.

(on camera): They liked to get noticed? RAJA NAGESWARAN, FRIEND OF SUSPECTS: Yes.

I mean, they had a black car. And I saw their car multiple times last semester. And it was very noticeable because they played loud music in their cars. And they used to screech their tires all the time. I felt that they wanted to be noticed.

TODD (voice-over): Nageswaran didn't know suspect Robel Phillipos, but says he knew Kadyrbayev, Tazhayakov and Dzhokhar Tsarnaev from the parties they all went to.

(on camera): What were they like socially?

NAGESWARAN: They were social animals. They used to dance. They used to drink. And they also liked to play games together with other people.

TODD: What kind of games?

NAGESWARAN: Like "FIFA."

(CROSSTALK)

TODD: Like video games.

NAGESWARAN: Yes, video games.

TODD (voice-over): The criminal complaint says Dias Kadyrbayev was close enough to Dzhokhar Tsarnaev that he repeatedly visited Tsarnaev's home and met his family members. Court members say Azamat Tazhayakov once set off fireworks on the banks of the Charles River with Tsarnaev and that Tsarnaev told the two Kazakhs a month before the marathon attack that he knew how to make a bomb.

But there's no indication that any of the three arrested students knew about the marathon plot. Before he was accused of obstruction, Azamat Tazhayakov's father said he couldn't be involved.

AMIR ISMAGOULOV, FATHER OF AZAMAT TAZHAYAKOV (through translator): We were shocked. Everyone knows my son. He's never fought anyone. He's never been in touch with any radicals.

TODD: Phillipos and Dzhokhar Tsarnaev were in the class of 2011 at Cambridge Rindge and Latin School. All four young men enrolled at UMass Dartmouth later that year.

In a video we believe he posted on YouTube, Robel Phillipos describes his background in Cambridge.

ROBEL PHILLIPOS, SUSPECT: I grew up in a very mild-mannered way of living. I wasn't too poor. I wasn't too rich. I was an average guy.

TODD: Now friends are trying to piece together how three average guys got caught up in the marathon bombing investigation, and may wind up in prison. Was it a calculated attempt to deceive investigators? Nageswaran thinks it may have been just a clumsy effort to help a friend.

NAGESWARAN: They might have been scared initially, because they're international students. They may have panicked.

(END VIDEOTAPE)

TODD: And his -- their arrest has unsettled this college campus once again, less than two weeks after law enforcement agencies swarmed this campus and evacuated it right around the time of Dzhokhar Tsarnaev's capture -- Wolf.

BLITZER: And you're getting some more information on the third person who was arrested yesterday, the American, Phillipos. What are you learning?

TODD: Well, Wolf, it's interesting. He gave up some serious responsibility when he came here to the college.

And, of course, with his arrest, that responsibility is left in question. A friend told "The Boston Globe" that in recent years, Robel Phillipos helping his single mother care for some younger family members, and that because of that he would not go to parties when Dzhokhar Tsarnaev would go to parties. He would avoid going to parties. He really took some responsibility.

Not clear what happens to his family now that he's in jail.

BLITZER: You know, we're also just learning, Brian, that the laptop that -- the laptop that had been missing, that we now know the FBI had, the laptop belonging to Dzhokhar Tsarnaev, the younger brother, it was actually turned over to federal authorities by Dias Kadyrbayev, one of these Kazakh students. That's what we're just learning.

This laptop, Brian, and you have been looking into it, it potentially has a treasure trove of evidence inside.

TODD: There's no telling what could be on that laptop, Wolf.

It could be anything from items about bomb-making to anything else, you know, maybe some logistics involving the alleged plot, things like that. And that's clearly what law enforcement is going to be combing over, is combing over right now. And it also may establish further links between these suspects and Dzhokhar Tsarnaev.

There may not be any further links, but if there are, maybe you can find them on that computer. So, that's a key piece of evidence that they now have in their possession.

BLITZER: They're hoping to get some more cooperation from the widow of the elder Tsarnaev brother, Katherine Russell. They're hoping to get some more information from her as well.

Up next, residents flee an out-of-control wildfire in Southern California that's closed part of the Pacific Coast Highway. Look at these pictures coming in from our affiliates out there. We're going there live.

Plus, chilling images of the final seconds of a doomed flight, do they contain clues about what caused the fiery and the deadly crash?

(COMMERCIAL BREAK)

BLITZER: Happening now: a wildfire burning out of control in Southern California. It exploded from 10 acres to more than 6,000 acres in just five hours today, forcing evacuations, closing part of the Pacific Coast Highway.

CNN's Paul Vercammen is Newbury Park. That's northwest of L.A.

Paul, what's the latest there?

PAUL VERCAMMEN, CNN SENIOR PRODUCER: Well, right now in this neighborhood, this upscale neighborhood, Newbury Park, they're breathing a bit of sigh of relief.

But you can see, Wolf, right over here flames once again starting up. They have encircled this neighborhood entirely. Some of this, by the way, partly, an intentional burn by firefighters. They are using fire to fight fire. And they're going to burn again in this neighborhood soon.

You look over this hill, another plume of smoke. And as we take you wide over here, I'm going to go ahead and pivot, you can tell that this brushfire is nowhere near being contained. In fact, it has zero percent containment. And all of the smoke back over here in distance is also dark, indicating that brush fuel is burning.

So, they have got a lot of work to do. But the good news, the silver lining in all of these clouds is, so far, so far, from what we understand, none of these houses has burned. Yes, there have been some R.V.s that burned down and there's been some charred buildings, but they haven't lost any of the homes.

It's been an absolutely valiant effort by something like 600 firefighters to get in here. You can see the trucks down the street literally in the backyards making sure that these houses don't burn down. The homeowners deserve a lot of credit. Most of them put in what you would call defensible space, Wolf, so the fire wouldn't burn up their houses.

And there was a very tense moment earlier today -- right now, a little calmer here in Newbury Park -- back to you, Wolf.

BLITZER: All right, good to hear that, Paul. We will stay in close touch with you, Paul Vercammen on the scene. Coming up here in THE SITUATION ROOM: North Korea sentencing an American to 15 years of hard labor. Is Kim Jong-un trying to use him as a pawn?

And archaeologists make a stunning discovery that appears to solve a 400-year-old mystery that goes back to America's beginnings.

(COMMERCIAL BREAK)

BLITZER: Happening now: a surprising reaction to the idea of a face-to-face meeting with North Korea's Kim Jong-un. Stand by. See the look on the NATO secretary-general's face when I asked him that question.

Plus, a possible cause of a fiery 747 crash. Was an overloaded cargo hold to blame?

And a skull leads archaeologists to expose a shocking secret about America's earliest settlers and what they had to do to survive.

I'm Wolf Blitzer. You're in THE SITUATION ROOM.

An American citizen sentenced to 15 years hard labor in North Korea. A senior U.S. official tells CNN the man is a tour operator who had a visa to be in North Korea. But officials there accuse him of, quote, "hostile acts." CNN's senior international correspondent, Dan Rivers, is working the story for us. He's in Seoul, South Korea, right now.

What are you finding out, Dan?

DAN RIVERS, CNN SENIOR INTERNATIONAL CORRESPONDENT: It's an amazing case, amazing how little we know about what Kenneth Bae is alleged to have actually done. All we know is they say that he's done something, that committed hostile acts towards the regime.

It took the regime more than six months to put this case on trial. But the actual hearing only lasted two days. And he was sentenced on the same day without any right to appeal, to 15 years' hard labor inside North Korea. Many people now worried that Kenneth Bae is the latest bargaining chip in North Korea's high stakes game of brinkmanship.

(BEGIN VIDEOTAPE)

RIVERS (voice-over): There is curiously little information about Kenneth Bae online. Just this Facebook page started by his friends campaigning for his release from the secretive regime. He's been jailed for 15 years hard labor for, quote, "his crimes aimed to topple North Korea." The official news agency claiming, quote, "His crimes were proved by evidence," a possible reference to material reportedly found on a hard drive.

One of Bae's friends suggesting it may have been as innocuous of photos of orphans begging. Whatever he's done, or hasn't done, experts say he's now a bargaining chip for new leader Kim Jong-un. JASPER KIM, ASIA-PACIFIC GLOBAL RESEARCH: I think North Korea kind of looks at any U.S. citizen in and around North Korea as a mere asset, a commodity that can be traded in the open market. And so Kenneth Bae was just at the wrong place at the wrong time.

RIVERS: And Bae's not the first. Scenes like this are becoming all too familiar. Emotional captives reunited with their families, accompanied by a high-profile politician.

This was 2009, journalist Laura Ling and Euna Lee celebrate freedom. Former President Bill Clinton takes the credit. A year later it's a different former president, Jimmy Carter, with another relieved American, Aijalon Gomez.

Kenneth Bae is the sixth American in the wrong place at the wrong time. And the North Koreans may once again be holding out for a high- profile visitor before they give him up.

(on camera): What North Korea wants above all else is to enter one-on-one talks with the United States; to gain concessions and get an end to punitive actions. They may see Kenneth Bae as the perfect way to achieve that aim.

(voice-over): With the announcement of their third successful nuclear test in February, the stakes couldn't be higher. North Korea even threatened a preemptive nuclear strike during South Korean/U.S. war games last month. Those maneuvers are over, but it seems the brinkmanship is not.

(END VIDEOTAPE)

RIVERS: Well, there's been a lot of speculation here, Wolf, that former president, Jimmy Carter, will be the one to get the call up to sort this situation out. Well, I've heard back from his spokeswoman. She says that he has not had an invitation to visit North Korea and has no plans to visit. So they're going to have to look elsewhere if they want to get Kenneth Bae released -- Wolf.

BLITZER: Sure a lot of people want to do exactly that. Dan Rivers in Seoul, thanks very much.

And by the way, coming up at the top of the hour, for our viewers here in North America, Erin Burnett is talking with Euna Lee. She's the American journalist who was held captive in North Korea before former president, Bill Clinton, was able to negotiate her release. That's 7 p.m. Eastern, "ERIN BURNETT OUTFRONT."

Earlier I had a chance to speak about the standoff with North Korea with the NATO secretary-general, Anders Fogh Rasmussen.

(BEGIN VIDEOTAPE)

BLITZER: You were recently on the Korean Peninsula. Why do you believe Kim Jong-un, the North Korean leader, and his forces have not gone ahead with this missile launch, this missile test that they boasted about so publicly in recent weeks? ANDERS FOGH RASMUSSEN, SECRETARY-GENERAL, NATO: Well, I will refrain from guessing about motives and intentions in Pyongyang. I, as you said, visited Korea recently. And NATO has a very key position. We have strongly condemned the provocative actions and the provocative rhetoric of the North Korean regime. And we consider that provocative behavior, a threat to the region and international security and stability. And we urge the leadership in North Korea to comply with the relevant U.N. resolutions.

BLITZER: Would you meet with Kim Jong-un?

RASMUSSEN: No, that's not in the cards.

BLITZER: Secretary-General, thanks very much for coming in.

RASMUSSEN: You're welcome. Thank you. My pleasure.

(END VIDEOTAPE)

BLITZER: We're following also other news, including the investigation into the fiery crash of a 747 cargo plane in Afghanistan that killed seven Americans. The stunning video of the plane falling from the sky has gone viral. It may provide some important clues. CNN's Pentagon correspondent, Chris Lawrence, has the latest -- Chris.

CHRIS LAWRENCE, CNN PENTAGON CORRESPONDENT: Well, Wolf, we may be getting closer to hearing why this 747 crashed. The NTSB go team arrived in Afghanistan today, along with representatives from the FAA and Boeing, the company that built the plane.

(BEGIN VIDEOTAPE)

LAWRENCE (voice-over): There were thunderstorms in the area when the Boeing 747 purportedly shown here stalled and crashed in Afghanistan. So weather is one potential cause. Weight is another.

STEVEN WALLACE, FORMER FAA OFFICIAL: The overall weight has to be within the center of gravity limits. The cargo ships in either direction, it's possible that it could go out of the limits.

LAWRENCE: So it's not just the total, but where that weight is positioned on the plane.

As part of the drawdown in Afghanistan, the U.S. has been removing a massive amount of heavy equipment. So this 747 takes off for Dubai with five armored vehicles onboard. Each weighs 13 tons and has to be locked in a certain spot. But if one of the chain attachments were to fail, one loose vehicle could suddenly push 20, 30 tons to the rear of the plane.

(on camera): A lot of people sitting at home are wondering what's the difference between this flight and a 747 that they might get on?

WALLACE: Well, this is a 747 400. It is a very widely-used commercial passenger airplane with an excellent safety record. LAWRENCE (voice-over): And whether you're flying tourist to Australia or hauling gear from Afghanistan, balance is essential. Even carrying the Space Shuttle Discovery on its back, this 747 weighs less than 500,000 pounds. Compare that to the same plane with hundreds of seats, passengers, luggage and food. It can weigh more than 800,000 pounds.

The airlines are so precise, they add five pounds to the average passenger's weight in winter, to account for heavier coats and boots.

(END VIDEOTAPE)

The differences are the steep takeoff, and more importantly, that it would be much more difficult for massive amounts of weight to shift so quickly on a passenger plane -- Wolf.

BLITZER: Reporting for us, pretty scary stuff. Thank you.

Coming up inside the mind of a killer. Could biology explain the motives for the Boston Marathon bombings. Our Dr. Sanjay Gupta is investigating.

Plus, a crowning achievement at the new World Trade Center.

(COMMERCIAL BREAK)

BLITZER: We've just confirmed that the body of the suspected killer in the Boston terror attacks, Tamerlan Tsarnaev, the body has now arrived at a funeral home in Boston. There you see video that we got from our affiliate, WCVB.

Earlier, a spokesman for the Massachusetts office of the chief medical examiner said that the body was claimed. Did not say who claimed the body, only that it would be taken to a funeral home. He would not release any additional details. But now we know the body is at the funeral home.

We do anticipate the cause of death, the certificate to be released sometime tomorrow morning. We'll have coverage of that here on CNN tomorrow.

Some important clues, potentially, in the Boston bombing investigation may actually lie inside the brains of the suspect's possible abnormalities that experts say could have predisposed them to this kind of horrific attack. Here's our chief medical correspondent, Dr. Sanjay Gupta.

(BEGIN VIDEOTAPE)

DR. SANJAY GUPTA, CNN CORRESPONDENT: In the wake of tragedy come the inevitable questions: What makes a killer. Is there a switch that turns on a rampage? And why? Why would someone do this?

ADRIAN RAINE, UNIVERSITY OF PENNSYLVANIA: You can just say the person's evil. I think that's 13th century thinking. I think we've moved beyond that. GUPTA: Adrian Raine is a criminologist. He's also the author of a new book, "The Anatomy of Violence." He spent more than three decades studying cold-blooded killers. He says there are biological explanations for violence. And Raine is convinced that brain dysfunction may, in part, explain the terror unleashed in Boston.

RAINE: Were they just completely normal people who just decided one day, you know what? We want to create mayhem. I don't think so. I think it's more complicated than that.

GUPTA: Raine says he first saw echoes of his own work with violent criminals when this image of 19-year-old suspect Dzhokhar Tsarnaev was released.

RAINE: While others were running away, he was just walking away as cool as a cucumber. I mean, that really struck me. Because I've seen this before in psychopaths and murderers in prison.

GUPTA: Then there were these photos of the brother who was killed, Tamerlan Tsarnaev, boxing.

RAINE: We've found a neurological abnormality in the brain that predisposes to violence and psychopathy. And it's also been found in boxers.

This is called cavum septum pellucidum. During cranial (ph) development, as the limbic regions begin to expand and develop, they compress or fuse the two leaflets of the septum pellucidum together. For some people, because of maldevelopment of the limbic system, the gap never closes.

It gives rise to a lack of fear and a psychopathic-like personality who could go and kill, you know, a number of people, and maybe not have any sense of shame or remorse or guilt about doing that.

GUPTA: Now another seat of fear in the brain is this almond- shaped structure over here called the amygdala. This is the brain of a psychopath. According to Raine's studies, these blue areas over here, they shrink in psychopaths, and it makes the amygdala area dramatically smaller.

RAINE: This part of the brain is very much involved in fear conditioning. You experience when you are thinking of doing something, that's not right. And then you get that awful feeling, "No, I shouldn't do that." If that's broken, then perhaps an individual is more likely to perpetrate a horrific act like the Boston bombings.

(END VIDEOTAPE)

BLITZER: And Sanjay's joining us right now. How difficult -- difficult was it, Sanjay, for the expert to discuss these alleged bombers without actually examining their brains?

GUPTA: Yes, it's -- I mean, there is sort of an emerging science quality to this, Wolf. I mean, one thing that Adrian Raine has looked at a fair amount is serial killers. He has -- evidence on terrorists, being able to look into the brains of people who commit mass rampage like this, that's harder data to come by.

So he's looking for similarities, for example, between these serial killers and people who commit terrorism and seeing if there are some -- some commonalities there. So it's not, you know, ironclad by any means. It's an emerging science, but he's the guy sort of trying to investigate this.

BLITZER: What about the role of genetics? The two Tsarnaev brothers obviously related. Is there a connection here in genetics and violence, if you will?

GUPTA: When you ask researchers who look at, OK, how much is biology and how much of this is environmental, you get back the answer often. It's about 50/50. You know, there's 50 percent maybe related to genetics.

And when you talk about brothers like this, obviously this becomes a very germane question. Two ways they sort of try and examine this, Wolf. One is to look at identical twins and try and figure out identical twins who may have been raised in different circumstances, what are the commonalities in terms of personality type, in terms of essential aggression, obviously if there's a criminal record.

But also people who have been adopted, Wolf. Here the question becomes, if they were raised in a good home, they had an upbringing that did not raise any red flags, and yet they still developed some sort of criminal behavior, going back and looking at the birth parents and trying to figure out, you know, just how much of a role each played. But I think, you know, right now, it's safe to say genetics plays a pretty significant role. They say about half and half, Wolf.

BLITZER: Interesting stuff. Sanjay, thanks very much.

GUPTA: You got it, Wolf. Thank you.

And to our viewers, you can learn a lot more from Sanjay and his expert, Adrian Raine, this weekend on Sanjay's Emmy-nominated "SANJAY GUPTA M.D." Here in the United States, it airs twice -- Saturdays, 4:30 p.m. Eastern; Sundays, 7:30 a.m. Eastern -- only here on CNN.

Up next, a new discovery in a 400-year-old mystery that goes back to America's earliest settlers. A shocking secret revealed.

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BLITZER: Archaeologists appear to have solved a 400-year-old mystery that goes back to America's roots. It's a startling discovery about the way some early settlers apparently survived a very brutal winter while others starved. CNN's Lisa Sylvester has the story.

(BEGIN VIDEOTAPE) LISA SYLVESTER, CNN CORRESPONDENT (voice-over): They came by ship with their hopes. Jamestown, the first permanent English settlement in North America in 1607.

It was long believed that James Fort on the island had over time washed away. But in 1994, archaeologists working in the area started finding the remains of the original fort.

And then something even more astounding was discovered last year. Archaeologists say this skull belonged to a 14-year-old girl of European descent. This is what they believe she looked like. They are calling her Jane.

She was on board a ship that arrived in 1609. It couldn't have been at a worse time. The food supplies they were bringing from England were lost or spoiled in a severe storm, and tensions were high between the Powhatan Indians and the settlers.

JAMES HORN, VICE PRESIDENT OF RESEARCH, COLONIAL WILLIAMSBURG: The fort is cut off. It's besieged by the Powhatans and these 300 men, women and children are trapped within the confines of the fort itself.

SYLVESTER: For hundreds of years, it's been a mystery: how did the settlers survive? They had only enough food to last two months, just as winter was setting in. A winter known as the starving time of Jamestown. No food, disease, and war.

JAMES KELSO, JAMESTOWN REDISCOVERY PROJECT: In the records, there were accounts of the fact that, when things were so desperate and it was very hopeless for the colonists, that they resorted -- some resorted to cannibalism. But they were kind of enigmatic references. Some believed it; some didn't.

SYLVESTER: But now they say they have evidence: the skull. It was found in an abandoned cellar of the fort. Douglas Owsley is a world-famous forensic anthropologist. He says the cuts on Jane's jaw were from a very sharp knife consistent with efforts to remove flesh, consistent with cannibalism.

DOUGLAS OWSLEY, SMITHSONIAN NATIONAL MUSEUM OF NATURAL HISTORY: I can tell you the violence in terms of the mutilation of the bones, the fracturing, there's no way that this is just trauma. They have a very clear intent, and the clear intent in this instance is the need to remove tissues for consumption.

KELSO: This discovery really, to me, has made such an impact on my empathy with the hardships that the settlers went through for that time period and how close Jamestown came to failing. If it failed, the course of American history would be very different.

SYLVESTER: November of 1609, there were 300 settlers. By the time more provisions arrived the following spring, there were only 60 settlers left.

(END VIDEOTAPE) SYLVESTER: The new exhibition telling Jane's story and the fate of the settlers opens tomorrow in Jamestown, Virginia.

Historians and anthropologists, they are now trying to find out Jane's true identity by poring through historical documents and archives. But at this point it's not known if she was the daughter of a gentryman or if she was a servant. And Wolf, they don't know at this point even how she died.

BLITZER: Looks like a 400-year-old mystery, though, has been solved.

SYLVESTER: Yes. I mean, if you think about everything that they had to go through, they were cut off by the Indians. They couldn't leave the fort, and they somehow had to survive, and some of them did, Wolf.

BLITZER: Good report. Thanks very much for the historical analysis.

Up next, the crowning achievement in the rebuilding of Ground Zero more than a decade after 9/11.

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BLITZER: On board this helicopter, Pope Emeritus Benedict XVI returned to the Vatican the first time since his resignation. Today he moved into a renovated convent in the Vatican gardens where he plans to spend the rest of his life.

Also on the move, one of the final pieces from the tallest building in the Western Hemisphere which is helping New York City to rise from the ashes of Ground Zero. Here's CNN's Jeanne Moos.

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JEANNE MOOS, CNN CORRESPONDENT (voice-over): It's what people record. The star on top of the tree. The ball above Times Square. And now New York's newest ornament has been lifted, the spire that will top off One World Trade Center.

The antenna on the old World Trade Center was the last thing to come crashing down. And now we've come full circle with a new spire going up, an American flag attached. For the construction workers...

PHIL DUCATELLI, WTC CONSTRUCTION WORKER: To see this go up and cap it off, it's a beautiful moment for everybody. You know, not just for New Yorkers, for America.

MOOS: Workers applauded as the spire was lifted. It will serve as a broadcast transmission center. There will be a beacon on top.

STEVE PLATE, WTC CONSTRUCTION WORKER: The beacon that will be seen for miles around and give a tremendous indication that we're back and we're better than ever. MOOS: Workers on lower floors took pictures as the spire was hoisted past them, atop the 104-floor building. Workers savored the moment with upraised arms and dangling feet.

UNIDENTIFIED MALE: You can't knock us down. Because we just keep on getting up and doing what we have to do.

MOOS: A giant crane lifted the 22-ton section. The spire, when fully installed, will bring the building to a height of 1,776 feet, the date America declared its independence.

This was the view from up there with the spire looking like a rocket suspended over Manhattan. Liftoff.